Thiazolo[5,4-d]pyrimidines and oxazolo[5,4-d]pyrimidines can be considered as structural analogues of purines, in which the imidazole moiety is replaced by a 1,3-thiazole or 1,3-oxazole ring system. Although purine chemistry is extensively described in literature, the number of medicinal chemistry papers that describe the synthesis and biological evaluation of oxazolopyrimidines and thiazolopyrimidines is limited. Apparently, the oxazolopyrimidine and thiazolopyrimidine scaffold is not very frequently used in drug discovery programs.
However, biological activities of certain thiazolo[5,4-d]pyrimidines and oxazolo[5,4-d]pyrimidines have been reported. 2,5-Diaminothiazolo[5,4-d]pyrimidin-7(6H)-one, a thio-isostere of 8-amino-guanine, was found to be a weak inhibitor of purine nucleoside phosphorylase (J. C. Sircar et al. J. Med. Chem. 1986, 29, 1804-1806). Thiazolo[5,4-d]pyrimidines were covered by several patent applications as activators of caspases and inducers of apoptosis (WO2008/057402), anti-angiogenic agents (WO2004/01314), growth factor receptor inhibitors (EP1731523), heat shock protein 90 inhibitors (WO2008/059368) and xanthine oxidase inhibitors (WO2007/004688). WO2008/152390 discloses thiazolo[5,4-d]pyrimidines and their use as inhibitors of phosphatidylinositol-3 kinase. WO 2008/005303 discloses vanilloid receptor 1 (TRPV1) modulating thiazolo[5,4-d]pyrimidine analogues and their use for the treatment of diseases, such as pain, arthritis, itch, cough, asthma, or inflammatory bowel disease.
2-Aryloxazolo[5,4-d]pyrimidines have been described as adenosine kinase inhibitors (M. Bauser; et al. Bioorg. Med. Chem. Lett. 2004, 14, 1997-2000). 7-Amino-5-phenylethylamino-2-furyl-oxazolo[5,4-d]pyrimidines act as brain A2A adenosine receptor (A2AAR) antagonists (M. H. Holschbach, et al. Eur. J. Med. Chem. 2006, 41, 7-15). 7-(Substituted-cyclopentyl)aminooxazolo[5,4-d]pyrimidines have been reported to possess tumor growth inhibitory activity (WO/2008/019124). However none of these documents teaches or suggests thiazolo[5,4-d]pyrimidine or oxazolo[5,4-d]pyrimidine derivatives having the substitution pattern disclosed by the present invention.
A huge number of thieno[2,3-d]pyrimidines is already known in the art. WO 2007/102679 discloses thienopyrimidines with at position 4 a pyrrole-2,5-dione substituent which strongly inhibits IKB kinase-β (IKK-β) involved in the activation of a transcriptional factor, NF-κB, which is associated with inducing various immune and inflammatory diseases, whereby a composition comprising the compound is a useful therapeutic agent against inflammatory diseases, in particular, arthritis and cancer. WO 2007/084815 discloses 2-carboxamide substituted thieno(2,3-d)pyrimidines inhibitors of one or more of the EGFR, HER-2, c-Src, Lyn, c-Abl, Aurora-A or VEGF kinase proteins and the like possessing anti-tumor cell proliferation activity, and as such are useful in treating or ameliorating a EGFR, HER-2, c-Src, Lyn, c-Abl, Aurora-A or VEGF kinase receptor mediated, angiogenesis-mediated or hyperproliferative disorder.
WO 2006/071988 discloses certain 4,5-disubstituted thienopyrimidine derivatives which are useful for the inhibition of PDE10 enzymes, and thus are useful for treating psychiatric or neurological syndromes, such as psychoses, obsessive-compulsive disorder and/or Parkinson's disease. WO 2004/111057 discloses compounds which are particularly useful for inhibiting potassium channels Kvl. 5), which are known targets for the treatment of cardiac arrhythmia in the atria such as atrial fibrillation. However, none of these documents teaches or suggests thieno(2,3-d)pyrimidine derivatives having the substitution pattern disclosed by the present invention.
Marketed drugs with a purine based skeleton are known. Examples include theophylline (drug for the treatment of asthma) and azathioprine (drug for the treatment of transplant rejection). Anti-cancer drugs with a purine scaffold include 6-mercaptoguanine and thioguanine. Purines are also an important constituent of antiviral nucleosides such as acyclovir (used for the treatment of herpes virus infections) and ganciclovir (medication used for treatment of cytomegalovirus infections). Abacavir and dideoxyadenosine (ddA) are both purine nucleosides acting as reverse transcriptase inhibitors and both compounds are licensed as anti-HIV agents.
Purines display a broad range of biological activities and as a result a huge number of purine analogues is already known in the art. WO 2009/005687 discloses purine derivatives and their use as modulators of Toll-like receptor 7. Compounds and pharmaceutical compositions which selectively activate toll-like receptor 7 are useful for treating viral infections in patients. WO 2008/135232 relates to substituted purines and purine derivatives as inhibitors of Aurora A, Aurora B, Aurora C, CHK2, JNK1 α1, JNK3 and abl kinase. These compounds possess antiproliferative properties and are useful in the treatment of proliferative disorders such as cancer, leukemia, psoriasis and the like. WO 2008/094737 discloses purine derivatives as inhibitors of calcium dependent protein kinase 1 (PfCDPKI). These purines are useful for treating malaria. WO 2008/090181 relates to a new series of purine derivatives as inhibitors of Janus kinases. JAK3 kinase inhibitors have been recognized as a new class of effective immunosuppressive agents useful for transplant rejection prevention and in the prevention or treatment of immune, autoimmune, inflammatory and proliferative diseases such as psoriasis, psoriatic arthritis, rheumatoid arthritis, multiple sclerosis, inflammatory bowel diseases, systemic lupus erythematosus, type I diabetes and complications from diabetes, allergic reactions and leukemia. WO 2008/060301 also discloses 7-substituted purine derivatives as immunosuppressive drugs useful for treatment of an autoimmune disease, an inflammatory disease, a mast cell mediated disease, hematological malignancy and organ transplant rejection. However none of these documents teaches or suggests purine derivatives having the substitution pattern disclosed by the present invention.
However there is a continuous need in the art for specific and highly therapeutically active compounds, such as, but not limited to, drugs for treating immune and autoimmune disorders, organ and cells transplant rejections. In particular, there is a need in the art to provide immunosuppressive compounds, which are active in a minor dose in order to replace existing drugs having significant side effects and to decrease treatment costs.
Currently used immunosuppressive drugs include antiproliferative agents, such as methotrexate (a 2,4-diaminopyrido(3,2-d)pyrimidine derivative disclosed by U.S. Pat. No. 2,512,572), azathioprine, and cyclophosphamide. Since these drugs affect mitosis and cell division, they have severe toxic effects on normal cells with high turn-over rate such as bone marrow cells and the gastrointestinal tract lining. Accordingly, marrow depression and liver damage are common side effects of these antiproliferative drugs.
Anti-inflammatory compounds used to induce immunosuppression include adrenocortical steroids such as dexamethasone and prednisolone. The common side effects observed with the use of these compounds are frequent infections, abnormal metabolism, hypertension, and diabetes.
Other immunosuppressive compounds currently used to inhibit lymphocyte activation and subsequent proliferation include cyclosporine, tacrolimus and rapamycin. Cyclosporine and its relatives are among the most commonly used immunosuppressant drugs. Cyclosporine is typically used for preventing or treating organ rejection in kidney, liver, heart, pancreas, bone marrow, and heart-lung transplants, as well as for the treatment of autoimmune and inflammatory diseases such as Crohn's disease, aplastic anemia, multiple-sclerosis, myasthenia gravis, uveitis, biliary cirrhosis, etc. However, cyclosporines suffer from a small therapeutic dose window and severe toxic effects including nephrotoxicity, hepatotoxicity, hypertension, hirsutism, cancer, and neurotoxicity.
Additionally, monoclonal antibodies with immunosuppressant properties, such as OKT3, have been used to prevent and/or treat graft rejection. Introduction of such monoclonal antibodies into a patient, as with many biological materials, induces several side-effects, such as dyspnea. Within the context of many life-threatening diseases, organ transplantation is considered a standard treatment and, in many cases, the only alternative to death. The immune response to foreign cell surface antigens on the graft, encoded by the major histo-compatibility complex (hereinafter referred as MHC) and present on all cells, generally precludes successful transplantation of tissues and organs unless the transplant tissues come from a compatible donor and the normal immune response is suppressed. Other than identical twins, the best compatibility and thus, long term rates of engraftment, are achieved using MHC identical sibling donors or MHC identical unrelated cadaver donors. However, such ideal matches are difficult to achieve. Further, with the increasing need of donor organs an increasing shortage of transplanted organs currently exists. Accordingly, xenotransplantation has emerged as an area of intensive study, but faces many hurdles with regard to rejection within the recipient organism.
The host response to an organ allograft involves a complex series of cellular interactions among T and B lymphocytes as well as macrophages or dendritic cells that recognize and are activated by foreign antigen. Co-stimulatory factors, primarily cytokines, and specific cell-cell interactions, provided by activated accessory cells such as macrophages or dendritic cells are essential for T-cell proliferation. These macrophages and dendritic cells either directly adhere to T-cells through specific adhesion proteins or secrete cytokines that stimulate T-cells, such as IL-12 and IL-15. Accessory cell-derived co-stimulatory signals stimulate activation of interleukin-2 (IL-2) gene transcription and expression of high affinity IL-2 receptors in T-cells. IL-2 is secreted by T lymphocytes upon antigen stimulation and is required for normal immune responsiveness. IL-2 stimulates lymphoid cells to proliferate and differentiate by binding to IL-2 specific cell surface receptors (IL-2R). IL-2 also initiates helper T-cell activation of cytotoxic T-cells and stimulates secretion of interferon-γ which in turn activates cytodestructive properties of macrophages. Furthermore, IFN-γ and IL-4 are also important activators of MHC class II expression in the transplanted organ, thereby further expanding the rejection cascade by enhancing the immunogenicity of the grafted organ. The current model of a T-cell mediated response suggests that T-cells are primed in the T-cell zone of secondary lymphoid organs, primarily by dendritic cells. The initial interaction requires cell to cell contact between antigen-loaded MHC molecules on antigen-presenting cells (hereinafter referred as APC) and the T-cell receptor/CD3 complex on T-cells. Engagement of the TCR/CD3 complex induces CD154 expression predominantly on CD4 T-cells that in turn activate the APC through CD40 engagement, leading to improved antigen presentation. This is caused partly by upregulation of CD80 and CD86 expression on the APC, both of which are ligands for the important CD28 co-stimulatory molecule on T-cells. However, engagement of CD40 also leads to prolonged surface expression of MHC-antigen complexes, expression of ligands for 4-1BB and OX-40 (potent co-stimulatory molecules expressed on activated T-cells). Furthermore, CD40 engagement leads to secretion of various cytokines (e.g., IL-12, IL-15, TNF-α, IL-1, IL-6, and IL-8) and chemokines, all of which have important effects on both APC and T-cell activation and maturation. Similar mechanisms are involved in the development of auto-immune disease, such as type I diabetes. In humans and non-obese diabetic mice, insulin-dependent diabetes mellitus results from a spontaneous T-cell dependent autoimmune destruction of insulin-producing pancreatic beta, cells that intensifies with age. The process is preceded by infiltration of the islets with mononuclear cells (insulitis), primarily composed of T lymphocytes. A delicate balance between auto-aggressive T-cells and suppressor-type immune phenomena determines whether expression of auto-immunity is limited to insulitis or not. Therapeutic strategies that target T-cells have been successful in preventing further progress of the autoimmune disease. These include neonatal thymectomy, administration of cyclosporine, and infusion of anti-pan T-cell, anti-CD4, or anti-CD25 (IL-2R) monoclonal antibodies. The aim of all rejection prevention and auto-immunity reversal strategies is to suppress the patient's immune reactivity to the antigenic tissue or agent, with a minimum of morbidity and mortality. Accordingly, a number of drugs are currently being used or investigated for their immunosuppressive properties. As discussed above, the most commonly used immunosuppressant is cyclosporine, which however has numerous side effects. Accordingly, in view of the relatively few choices for agents effective at immunosuppression with low toxicity profiles and manageable side effects, there exists a need in the art for identification of alternative immunosuppressive agents and for agents acting as complement to calcineurin inhibition.